Airborne Communications Node
1. Airborne Communications Node (ACN) is a DARPA program to design, develop,
integrate and demonstrate a prototype communications payload for airborne platforms. It
will provide enhanced Theater communications capability for on-the-move warfighters.
This multi-function payload enhances and augments eight essential warfighter
communications services.
ACN is modular, scalable and reprogrammable. It can be tailored to fill mission-specific
needs in command and control communications. ACN's flexibility also extends to the
platform it can be hosted on.
One of the target platforms for the ACN payload is the Global Hawk high altitude
endurance (HAE) unmanned air vehicle (UAV). However, the open system nature of the
design enables subsets of the eight services to be installed on alternate platforms such as
manned aircraft or helicopters, as desired by the Services.
2. The ACN will allow the warfighter access to a single, flexible, multi-function system,
regardless of the warfighter's environment. It will support the mounted and dismounted
soldier or marine on the ground, the pilot in the air, and the sailor at sea.
The goal of the ACN Program is to combine innovative solutions in advancing
technologies, and leverage evolving commercial capabilities into a single integrated
payload, providing communications services-on-demand for warfighters beyond line-of-
sight.
The ACN has the capability to serve as a gateway between disparate stove-pipe
communications systems and at the same time provide a high-speed, high-throughput
communications backbone in the sky.
3. ACN is not a unique, stove-pipe communications capability. Rather, it enhances and
augments the current mobile military communications infrastructure, by working with it.
By improving theater-wide communications, as well as, out-of-theater reachback, we
improve interoperability and information sharing -- all critical to achieving information
superiority.
An important benefit of the ACN is its ability to provide communications without needing
its own infrastructure there first. It is self-deployable -- at least to the extent that the
airborne platform is. By loitering over the theater, it provides an instant communications
capability for existing military radios on the ground, at sea, or in the air. In particular, it
avoids the necessity of bringing in heavy communications gear, such as MSE trucks and
SATCOM terminals, at times when transport to the theater is in short supply.
The ACN must be interoperable with legacy communication systems, and support growth
for new requirements, including joint and combined forces. It will be scaleable to match
the communication requirements of different missions; extendible to support growth and
change; and affordable over its life cycle.
4. The ACN will provide a self-sustaining wireless infrastructure that can support all units
within its line-of-sight. Small units, Special Forces, or major Corps-level forces can be
supported by single or multiple ACN's, depending on mission need. Although ACN does
not require a ground infrastructure to be in place to provide communications, it will interact
with and augment whatever in-theater assets are in place.
The ACN payload can be dynamically controlled and configured while in-flight. The
specific mix of services provided at any instant in time can be reprogrammed real-time by
an authorized user through any communications link. Or it can be autonomously
reconfigured, via a pre-established script. Because of this real-time reprogrammability,
ACN is adaptable to support rapidly evolving mission profiles.
5. The ACN will replace the hardware intensive designs of legacy radios with the newer
software-based radio designs, to accomplish waveform generation and processing,
encryption, and other major communication system functions.
ACN will use a modular concept to maximize the use of common hardware and software.
Ideally, we would like to have a generic bank of RF channels that are completely
interchangeable. If any channel can support any waveform or service we have a completely
reconfigurable system at the channel level.
The modularity of the ACN also allows the design to capitalize on evolving technologies
supporting miniaturization and scalability of product. Enabling the maximum capability in
the smallest package makes ACN easily platform adaptable.
6. The ACN payload is being designed to provide any-to-any connectivity among users and
services for both data and voice. This any-to-any connectivity also extends to other ACN
platforms through air-to-air crosslinks, and a self-organizing airborne backbone. The
payload will provide any required message or encryption translation and data buffering.
The routing of data from one service to another will be completed using enhanced
commercial routing protocols and through the establishment of virtual circuits (for non-
routed data and voice).
7. In order to dominate the future battlefield, we need to fight on-the-move. Maneuver
units executing high tempo operations require range extension, or area augmentation, for
their tactical communications systems, so they can maintain continuous connectivity with
their command elements.
The first of the 8 ACN services will provide range extension for over-the-horizon
connectivity for dispersed, isolated and rapidly moving forces. While particular focus will
be on extending the range of the tactical communications media that currently populate the
battlefield, (e.g. SINCGARS, Have Quick, EPLRS, Link 16 and MSE), ACN will be
capable of providing range extension for all current and future services.
8. While near-term ACN benefits are seen in improved operations of existing military
communications, there are also new services that can be provided by the CAN, through the
introduction of militarized commercial capabilities.
Among these are a theater paging service, using commercial-like receivers to alert users
who are out of normal communications contact; a rebroadcast capability for the Global
Broadcast System (GBS) that is adapted for forces on-the-move with a simple
omnidirectional receive antenna; and handheld radio communications similar to
commercial cellular or LEOSAT technology, but totally supported from an ACN ---
requiring no ground infrastructure.
Specifically, ACN provides:
• Militarized Personal Communications Service (PCS) circuit oriented voice and data
• Militarized tactical paging
• Internet-like data networking
• Tactical battlefield multicast
• High speed and high throughput airborne infrastructure with access both in and out-of-
theater
• Surrogate satellite support for ultra-high frequency tactical satellite and GBS receive/relay
• Interoperability among dissimilar radios
ACN's goal is to support all of these services (over 70 channels) simultaneously from a
single platform.
9. To make ACN really useful it needs to be small. The ACN SWAP objectives shown
here facilitate deployment of the payload as a package on the Global Hawk UAV. The
maximums represent the ACN payload utilizing all of the available Global Hawk capacity
(while maintaining altitude and mission duration). One of the goals of ACN is to make the
payload as small as possible. This would allow multiple payloads to be simultaneously co-
hosted on the Global Hawk, or an ACN could be put on a Predator or a Hunter UAV.
Although we used Global Hawk parameters to size our SWAP goals, it is important to
remember, that the ACN design will be modular and scaleable, so that it can be hosted on
other platforms.
At a 65,000 foot altitude, the ACN would be within line-of-sight of ground radios at ranges
out to 150 miles or more (depending on terrain), and ranges to other airborne platforms
could be 500 miles. Actual range for any given ACN will be dependent on the host
platform altitude.
10. The ACN program is being executed in two phases. The focus of Phase 1 is on
objective system design and risk mitigation.
In order to show the design feasibility to meet the thresholds and goals established for the
ACN, a series of demonstrations, tests, and experiments will be conducted as part of the
Phase 1 trades and design. These activities will show progress in addressing issues such as
component technology viability; subsystem performance; and size, weight and power
(SWAP). Phase 1 culminates with a proof-of-concept flight test on a manned aircraft.
The goal of Phase 2 of the ACN program is to integrate a fully functioning prototype
payload onto a Global Hawk, a subset payload onto a helicopter, and demonstrate military
utility in a joint Service exercise.
11. The technical challenges that must be met to implement the ACN functional capabilities
are significant. The most difficult is resolving the EMI/EMC problems that result from
integrating many radios and antennas on one platform. This problem is being addressed
through the development of technologies such as: advanced interference cancellation
systems, cosite managers, advanced antennas, and low-loss, multi-port antenna couplers.
Other technologies being developed within DARPA that are expected to be integrated into
an ACN design, include SiC power amplifiers, SiGe low-noise amplifiers, and advanced
filters.
12. So, how hard is this ACN interference mitigation problem? While there are frequency
hopping radios with cosite mitigation solutions on some of the current military C2
platforms, these are large, expensive and limited to supporting at most four simultaneous
channels. In our terminology here, each ACN channel represents an end-to-end connection
through the ACN. To meet the ACN thresholds and goals requires advancement in the
state-of-art in interference mitigation systems, both in number of channels supported, and
the SWAP per channel. The Phase 2 goal, illustrated here, is to support 20 simultaneous
VHF channels. This represents an order of magnitude increase in the number of channels,
coupled with an order of magnitude decrease in the SWAP.
13. In addition to the interference mitigation and SWAP, ACN must tackle several other
technical challenges.
The development of adaptive mobile communications --- able to maintain an end-to-end
QOS connection across multiple layers of mobile elements; and militarizing the evolving
commercial services, such as PCS and paging. All this must be accomplished, while
addressing the issues of security, robustness and supportability for the military
environment.
The rapid assimilation of leading edge information technology by the commercial market
permits the government to leverage commercial items for its military and civil applications.
The ACN must be architected in such a way that the DoD can modularly integrate these
developing technologies without sacrificing SWAP or autonomy.
14. The first phase of the ACN program began with the selection of three teams led by
Sanders, Raytheon and TRW, to develop designs capable of providing the maximum
number of services, within the SWAP, for a payload flyaway price of ~$5.0 M. The
program is being executed as a "Section 845" or "other transactions for prototype projects".
This acquisition approach enables a rapid and seamless transition from R&D to operational
use by the Services.
At the end of Phase 1, a down-selection to one team will be conducted. The selected team
will continue their efforts to develop, integrate and demonstrate a payload that meets the
thresholds and goals of the ACN. A multi-platform, Phase 2 flight demonstration, will be
conducted in conjunction with a joint Service military exercise.